Numerous neurotoxic side effects of cancer treatments include cognitive dysfunction, commonly called chemobrain and peripheral neuropathy. The mechanisms for these side-effects and ways to protect neurons remain to be elucidated. The DNA base excision repair (BER) pathway including the abasic- endonuclease1/redox factor (Ape1/Ref-1 or Ape1) has been shown to be the major DNA repair pathway for oxidative and alkylating agent damage that occurs with chemotherapy and ionizing radiation (IR). Additionally, Ape1 interacts with a number of transcription factors, especially NF:B, AP1 and p53 to regulate their function through redox signaling. In neurons, these transcription factors mediate the expression of a number of proteins involved in neuronal survival and altered excitability in response to injury and inflammation. Thus, Ape1 could play a critical role in maintaining homeostasis in neuronal tissue through its DNA repair and/or its redox function. The overall hypothesis of the proposed work is that Ape1 acts to enhance neuronal survival and function after injury by chemotherapy or IR and helps to maintain normal neuronal function by minimizing alkylation and oxidative damage to DNA as well as by regulating the activity of AP1, NFkB and p53. We will determine if Ape1 is involved in the neurotoxicity and neuronal function associated with chemotherapy and IR using primary rat central nervous system (hippocampal) and sensory neuronal cells (dorsal root ganglia or DRG). We will reduce or augment Ape1 expression in these neurons under normal and following the addition of cancer chemotherapeutic agents and IR and ascertain the effects on various aspects of neuronal function and survival. We also will use Ape1 mutant proteins that only have either the redox or repair functions or drugs that inhibit only the repair or redox activity to ascertain which functions of Ape1 are critical for neuroprotection/function. Finally, we will determine whether the redox activity of Ape1 alters the activity of downstream stress response factors such as AP1, NFkB and p53 in neuronal cultures following chemotherapy and IR.Experiments in this application will form the basis for mechanistic studies into neurocognitive ("chemobrain") and peripheral neuropathy experienced by patients following chemotherapy and IR. Understanding the mechanism for neuroprotection during cancer therapy will be critical in providing patients with neuroprotection that can help alleviate these serious side effects.